1. Field of the Invention
This invention relates to a process for the production of methylenedicarbanilates. More particularly, this invention provides a process for the production of methylenedicarbanilates; i.e., an intermediate product for use in the production of 4,4'-diphenylmethanediisocyanate which is generally called "MDI" and an important starting material for the production of polyurethanes.
2. Description of the Prior Art
MDI is used as a starting material for the production of polyurethane elastomers, elastic fibers, adhesives, coating resins, etc., and recently its production has been sharply increasing. At present, MDI is produced by a method which comprises reacting aniline with formaldehyde to give 4,4'-diaminodiphenylmethane and reacting the 4,4'-diaminodiphenylmethane with phosgene. This method, however, has the disadvantages in that the use of harmful phosgene is necessary, the phosgenation step is complicated, and that hydrochloric acid by-produced in the phosgenation step must be disposed of safely.
In addition to the phosgenation process, various methods have been proposed for the production of isocyanates, including: (1) a method in which aromatic carbamates are produced by reacting aromatic nitro compounds with carbon monoxide and alcohol in the presence of a catalyst comprising palladium, Lewis acid, e.g., iron chloride, and a heterocyclic base, e.g., pyridine [see Japanese Patent Application (OPI) No. 98240/1976 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application")] and then decomposed by heating; (2) a method in which the same reaction is carried out in the presence of a catalyst comprising palladium, vanadyl chloride and a heterocyclic base [see Japanese Patent Application (OPI) No. 22339/1979], and a method in which the same reaction is carried out in the presence of a catalyst comprising selenium, sulfur and a base [see Japanese Patent Application (OPI) No. 62420/1974].